In recent years, the energy depletion, the environmental pollution and the like have issued as global problems, and therefore hydrogen energy and fuel cells using the hydrogen energy have been increasingly used as a substitute of fossil fuel. Fuel cell transforms chemical energy of hydrogen into electrical energy. Fuel cell may use a variety of fuels, and pollutants are hardly generated. Furthermore, an energy saving effect is high due to the high power generation efficiency (40% or more).
These fuel cells may be widely used in the fields of various applications including transportations such as automobiles, ships, airplanes, etc.; power supplies such as electric generating plants, household power supplies, etc, and portable electric home appliances, etc.
The polymer fuel cell may be operated at room temperature and atmospheric pressure since it uses a solid polymer membrane having ion conductivity as an electrolyte. Also, the polymer fuel cell has come to the highlight as a power source for transportations, portable and household appliances, etc. since it has a low operating temperature (about 80° C.), a short operating time and a high power density.
In general, the solid polymer fuel cell includes a plurality of bipolar plates, each of them having a channel formed therein. Such bipolar plates are generally formed of one selected from the group consisting of graphite, carbon, Ti alloy, stainless steel and conductive plastics.
However, the bipolar plate formed of stainless steel has problems that interfacial contact resistance between a surface of the bipolar plate and a membrane-electrode assembly may be increased due to the semiconductive characteristics of a passivation layer formed in the surface of the bipolar plate.
Furthermore, the polymer fuel cell is operated under an acid atmosphere, but ion conductivity of an electrolyte membrane may be reduced due to the extraction of metal ions when the stainless bipolar plate does not ensure its corrosion resistance, and thereby an electrode catalyst may be polluted, which leads to deteriorate the performances of a fuel cell.